LITTLE ROCK, Ark. — Walmart is having all sorts of promotions for the back-to-school season, but selling firearms isn’t one of them.

The world’s largest retailer said Friday an internal investigation determined without a doubt that the company was pranked when a photograph emerged on social media showing a sign reading “Own The School Year Like A Hero” atop a gun case in a store.

“We have definite proof it was a prank,” Walmart spokesman Charles Crowson told The Associated Press on Friday evening.

The photograph on social media included Walmart’s superhero-themed, back-to-school promotion with a gun rack in a sporting goods section. Initially, the company apologized and said the sign was being taken down but then began to question whether it had been there at all.

Crowson wouldn’t say what proof the company had: Was an image manipulated? Did a customer move a sign for a joke? Did an employee deliberately or inadvertently place the “Own the School Year” sign on the wrong display?

He acknowledged only that the photo wasn’t taken at a store in Evansville, Indiana, as had been originally suggested. He wouldn’t say where the image had been made — only that the mystery had been solved.

“This is a result of a collective effort by a number of associates who take things like this seriously,” he said.

After the post appeared this week, a number of people criticized the company on social media, expressing disgust. Among the samples: “Lemme just scoop my jaw off the floor” and “I’ve seen a lot of disturbing pictures of folks shopping at WalMart, but this tops them all.”

The company has at times been pressured by shareholders about its gun sales. A New York church, for instance, petitioned in 2014 to have a shareholder vote on whether the company should sell products that “endanger public safety and well-being.” The next year, the company said it would no longer sell high-powered rifles because of lower sales.

In 2006, the company stopped gun sales in about 1,000 stores — it has more than 4,500 nationwide — again citing a lack of demand.